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Unable to get turbulent flow using LES model

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Old   January 6, 2009, 09:38
Default Unable to get turbulent flow using LES model
  #1
Tang Jingwei
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Hi.

I tried running my 3D empty channel (basically a hollow cuboid) flow using the LES model.

After a few thousand runs of time step, I still get a laminar velocity magnitude contour. I tried lowering my viscosity such that my Reynolds number reaches 2e10, but the results are still the same.

Is there a reason for this?
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Old   January 6, 2009, 12:15
Default Re: Unable to get turbulent flow using LES model
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What are the conditions set at the inlet of your channel?
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Old   January 7, 2009, 01:26
Default Re: Unable to get turbulent flow using LES model
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Tang Jingwei
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Hi there.

Inlet and Outlet are set as periodic.

Mass flow rate = 1kg/s Inlet velocity = 1m/s

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Old   January 7, 2009, 05:09
Default Re: Unable to get turbulent flow using LES model
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Paolo Lampitella
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Hi,

try to set an initial condition with a random perturbation.

What is your maximum and minimum grid spacing in the 3 directions?
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Old   January 7, 2009, 05:27
Default Re: Unable to get turbulent flow using LES model
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ck3
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Dear Paolo Lampitella: I want to use Large Eddy Simulation (LES) of the Fluent code: http://cfd.me.umist.ac.uk/ercofold/d...77/test77.html

I require for your assistance concerning the launching of this technique because it's the first time that I use it, especially this two information: 1. Time step Size 2. Number of time step I can give you more detail, if you send me you e-mail.
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Old   January 7, 2009, 22:33
Default Re: Unable to get turbulent flow using LES model
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zongtwi
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Have you tried using a RANS based turbulence model, and see the flow behaviour? This will allow you to troubleshoot any problems relating to your physical setup of your case, and also more importantly you can use this result as the initial condition to your LES case.

To use it as the initial condition, the turbulence predicted needs to be superimposed onto the mean flow. This is done via a TUI command:/solve/initialize/init-instantaneous-vel

Then you change your turbulence model to LES and start your solution.

Hope that helps.
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Old   March 21, 2009, 18:59
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khelfi Djillali
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Quote:
Originally Posted by zongtwi
;155846
Have you tried using a RANS based turbulence model, and see the flow behaviour? This will allow you to troubleshoot any problems relating to your physical setup of your case, and also more importantly you can use this result as the initial condition to your LES case.

To use it as the initial condition, the turbulence predicted needs to be superimposed onto the mean flow. This is done via a TUI command:/solve/initialize/init-instantaneous-vel

Then you change your turbulence model to LES and start your solution.

Hope that helps.
after initialization, is what I must turn over towards boundary conditions for velocity or I pass directly to the iteration
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